Yes, I agree, what specifically is the OP looking to improve?
Before buying a lens you really should be asking yourself where your current kit lacks. Your kit lens covers the ranges that you are looking at. Do you need a faster lens because you cannot get the shutter speeds you need with the kit lens? Do you feel the pictures lack sharpness, contrast, etc?
Don't get me wrong, I know it's a kit lens and there is much better out there, but you have a budget to work within, so I'm suggesting to think carefully about how this purchase will make your photography experience a happier one. I find myself wanting this or that because of the reviews in forums, but if your budget isn't unlimited, you just want to be sure your really going to be expanding your capabilities in a way to justify the expense (relative to your budget).
If you really want to go wide, you need to look at something in the 10mm range. I have the Sigma 10-20 (cheaper one) and have been relatively happy with it. We have a Tamron 10-24 at work, and I (and my co-worker) feel it is too soft, even stopped down and manually focused on a tripod. Though this may just be perception. Either way, 10mm opens up a whole different perspective from the 18-55mm, if that is what you are after.